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This is a man's brain on testosterone

This story might make women smile and nod their heads. But it could also encourage men to say, "It's not my fault."

A group of university professors performed tests on 243 males, primarily college students, to determine the effect of testosterone, or "T," on a key brain function. The conclusion: Those who received a dose of testosterone on their bodies were more likely to make quick, impulsive decisions. They made more mistakes on the type of tests usually given for college entrance. And, although this wasn't part of the test, they could also commit more errors when making key life choices.

"Testosterone overrides judgment," said professor Gideon Nave, who teaches marketing at the Wharton School in the University of Pennsylvania and is an author of the study.

The students in the experiment who used "T" gel made 20 percent more mistakes than those in the control group who hadn't used testosterone. In academic terms, it amounted to the difference between a solid grade of B and a barely passing mark.

It could also serve as a warning to those watching cable-TV ads that ask if you "Want to be better in bed?" or that extol the benefits of "T" in bodybuilding. Numerous lawsuits against testosterone products claim that when used in excess by men -- who already have much more of it than women -- it may damage the cardiovascular system and cause other side effects.

Conducted by faculty of Wharton, Western Ontario University and the California Institute of Technology, the study is the largest of its kind thus far. The all-male participants were given either a topical testosterone gel or a placebo in the morning and were told to remove their upper-body clothing and smear it on their arms, shoulders and torso.

Several precautions were taken to ensure the results were accurate, including measuring the size of participants' hands to determine any effect from prenatal testosterone. Subjects were instructed not to bathe. Females were excluded from even dispensing the gel due to possible effects on the male participants' testosterone levels.

Rather than blood tests, saliva was used to view the testosterone's effect without heightening anxiety. The single dose of topical testosterone did the participants no harm, and its effects were gone in 36 hours.

The test subjects had to return that afternoon for a "Cognitive Reflection Test" (CRT). Simply put: It required the participant to stop and think about his answer. The questions, which weren't complicated, were the kind of mathematical brain teasers usually found in a daily newspaper next to the horoscope.

For example: "A bat and a ball cost $1.10 in total. The bat costs $1 more than the ball. How much does the ball cost?" The key is the word "more," and the correct answer is five cents. But the testosterone-fueled group tended to ignore this and say "10 cents." There were similar answers to other questions.

However, when the participants took a math test to quickly add sets of two numbers, "these same men performed normally," said professor Amos Nadler, who teaches finance at Ivey Business School and is also an author of the study.

The key difference might be that testosterone appeared to inhibit "prefrontal" brain activity, according to previous research cited in this study. "Prefrontal is the executive function of the brain," said Nadler. In other words, instead of making the decision at the highest level, testosterone could take you on an elevator ride down to the basement boiler room.

While professors Nave and Nadler pointed out some of the negative aspects of testosterone, they concurred that much more research was needed to "disentangle" the full effects of this naturally occurring steroid. They noted that while some activities require "cognitive recognition," in other circumstances testosterone was very useful, such as when fight or flight has to be decided instantaneously.

And in other cases, too. "Facilitation of rapid intuitive responses by 'T' could be biologically adaptive in contexts where reproductive success depends on instinct (for example, during copulation)," the study said.

"There's no clear right or wrong," said Nave. "But the test we used shows that -- in one mathematical case -- there is a clear right or wrong."

So should men take testosterone supplements? That depends. Some will want to be the nerd who runs the high-tech company. Others will simply say, "Start the evolution without me."

Ed Leefeldt is an award-winning investigative and business journalist who has worked for Reuters, Bloomberg and Dow Jones, and contributed to the Wall Street Journal and the New York Times. He is also the author of The Woman Who Rode the Wind, a novel about early flight.